Besides obvious problems like your computer's sound being muted,one possible cause is that your web browser does not support this.There are two entirely different techniques used to play the sound.Your computer has to support (at least) one of them for sound to work:
Most used nowadays: HTML5 WebAudio, since this has been availablein most web browsers since several years:
Firefox version 17 or later
Chrome version 10 or later
Safari version 6 or later
Opera version 15 or later
Edge (as supplied with Windows 10)
Unfortunately, Internet Explorer does not yet support this technology.
Essentially only for Internet Explorer, you can also use Java applets; for this, you neednot only a webbrowser, but also version 1.4.2 or newer of Java working on your computer.Try http://javatester.org/version.htmlto find out if you have Java and which version it is.You may need to enable Java applets per site; see here.Some WebSDR sites have disabled Java support; those sites can only be used with HTML5 WebAudio.
So, which one do you use?WebSDR sites try to detect what your browser can do.If HTML5 WebAudio is available, it will be used; otherwise, Java will be tried.
I'm using Chrome and don't hear audio (on some sites)!
Since version 71, Chrome does not allow every website to start playing audio,in order to stop annoying advertisem*nts.Chrome tries to guess whether you want audio or not, but doesn't always get it right.On some WebSDR sites, you'll get an "audio start" button, on some you don't.
At the top right, click the 4 vertical dots, and then Settings.
At the bottom, click Advanced.
Under "Privacy and security," click Site settings.
Select "Sound"
Select "Add" and enter "http://*"
(thanks to K9GL for these instructions)
Note that the above effectively disables Chrome's "autoplay" policy forall http sites. Although stopping automatic sound from advertisem*nts is a noble idea,I think Chrome's autoplay policy is fundamentally wrong. Instead of trying to guess whatthe user wants, the browser should simply ask the user whether he/she wants to allow thepage to play sound (and remember that for later visits, of course).
I'm using Safari and don't hear audio (on some sites)!
It looks like Safari does something similar to what Chrome does as described above. You can enable audio via Safari > Settings for this web site> Autoplay > Allow all Autoplay. (thanks to M0IFA for these instructions)
Only some WebSDR sites work; on others I get no sound and no waterfall.
Please have a closer look at which sites work and which don't.Is it such that only those on "unusual" ports (i.e., thosethat have a number like :8901 in their URL) work, while those withouta port number (those run on the default web server port 80) don't work?Or the other way around?
If only those on port 80 work, you're probably behind a firewall thatonly allows port 80 (and a few others). This is often the case in public WiFi networks and office networks.
If only those on ports other than 80 work, you're probably behind aweb proxy server, which doesn't know how to handle the (non-standard)audio and waterfall data streams. The proxy server may also be in your internetservice provider's network.
Can I use the WebSDR on a smartphone/tablet/etc.?
Yes, if there is a browser for your device which supports HTML5 WebAudio.
On Android devices, these include Firefox, Chrome and Opera (but not Opera-Mini);and even recent versions of Android's built-in browser should work.
On iPhones, iPads etc, you can use the built-in Safari browser,but only if you have iOS version 6 or later.
I'm using an iPhone/iPad and don't hear audio!
An issue with iPad (-like) devices is that they have two mute switches:one which affects music, youtube, etc., and one which affects systemsounds (like mail notification bleeps). Somehow, iOS treats the WebSDR audio as the latter.So please check that you haven't accidentally muted the system sounds.On some devices this is a software switch, on others it's a physical hardware switch.
How can I decode digital signals like PSK31, RTTY, etc.?
Can I decode DRM ("digital radio mondiale") signals?
No. These signals are 9 or 10 kHz wide, which is much more than the bandwidthstreamed from the WebSDR server to the clients. Decoding them serverside is not an option either, because of the CPU load for the server. Furthermore, I think most DRM programmes canalso be heard directly on the broadcaster's website, so there is not much reasonfor listening to them via a WebSDR receiver.
I get a warning that the WebSDR Java applets are "unsigned". What does that mean?
See here.
Can I specify the frequency and mode in the URL when linking to a WebSDR ?
While SDR's and radios are not illegal in most countries this is a reminder to professional and amateur security researchers to check that what you are doing is legal in your country.
The classes of license, from highest to lowest are: Amateur Extra Class, General Class, and Technician Class. Before receiving a license grant, you must pass an examination administered by a team of volunteer examiners (VEs).
Find an SDR receiver that covers 1–2 gHz or whatever the phone frequency is in your country using… You'll hear the transmissions but you won't be able to decode them. They are sent digitally and the data is encrypted.
While your home or car radio is designed to tune traditional AM or FM, an SDR dongle that you attach to your computer through your USB port can tune — with the appropriate software — shortwave, police, aircraft, or even CB radio channels.
You can transmit in the ISM bands without a license. There are still power restrictions which most SDRs won't exceed anyways. Yes, a general user/consumer can transmit in the ISM band without a license, but they are still required to use intentional transmitters which have been certified by the FCC.
The use of software in an SDR system allows for greater flexibility, reconfigurability, and scalability compared to traditional radio systems, which are typically implemented using hardware-based solutions.
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